Field of the Invention
The present invention relates to a fuel containing a lubricity additive for improving the lubrication properties of fuels, whether ground vehicle engine fuel (diesel) or jet fuel, and more particularly of diesel fuels with a low sulphur content.
It is well known that diesel fuels and jet fuels must have lubricating capabilities, for the protection of pumps, injection systems and any moving part with which these products come into contact in an internal combustion engine. With the intention of employing products which are increasingly pure and non-polluting, in particular devoid of sulphur, the refining industry has been led increasingly to improve its treatment processes for the removal of sulphur compounds. However, it has been observed that on losing sulphur compounds, the aromatic and polar compounds often associated were also lost, which caused a loss in the lubricating power of these fuels. Thus, beyond certain contents, the elimination of sulphur compounds from the composition of these products very substantially promotes the phenomena of wear and of failure of moving components in pumps and in injection systems. As regulations in many countries have imposed a limitation on the acceptable upper content of sulphur compounds in fuels of 0.05% by weight, in order to lower the emissions of polluting combustion gases from cars, lorries or buses, especially in urban built-up areas, these lubricating compounds must be replaced by other compounds which are non-polluting with regard to the environment but exhibit a sufficient lubricating power to avoid the risks of wear.
The literature also mentions that petrol fuels with a low sulphur content have a lubricating power which can prove to be insufficient to ensure good lubrication of the injection systems in new vehicles and can bring about a premature risk of wear.
Several types of additives have already been provided in order to solve this problem. Thus, antiwear additives have been added to diesel fuels, some of these additives being known in the field of lubricants, of the type of unsaturated fatty acid dimers and fatty acid esters, aliphatic amines, esters of fatty acids and of diethanolamine, and long-chain aliphatic monocarboxylic acids, such as described in U.S. Pat. Nos. 2,527,889, 4,185,594, 4,204,481 and 4,208,190. The majority of these additives exhibit a sufficient lubricating power but at concentrations which are much too high, which is very unfavourable economically for purchasing. In addition, additives containing dimeric acids, like those containing trimeric acids, cannot be employed in fuels feeding vehicles in which the fuel can be in contact with the lubricating oil, because these acids form, by chemical reaction with the detergents usually employed in lubricants, deposits which can accelerate the wear processes.
U.S. Pat. No. 4,609,376 recommends the use of antiwear additives obtained from esters of mono- and polycarboxylic acids and of polyhydroxylated alcohols in fuels containing alcohols in their composition.
In Patent GB 2,307,246, the product resulting from the reaction of carboxylic acid containing 10 to 60 carbon atoms, chosen from fatty acids or fatty acid dimers, with an alkanolamine, obtained by condensation of an amine or of a polyamine with an alkylene oxide, is preferred as lubricity additive.
It is preferable, in Patent GB 2,307,247, to employ an acid derivative, substituted by a least one hydroxyl group or one ester of polyols, or alternatively an amide of this acid.
Another route chosen is to introduce vegetable oils or their esters into the fuels, in order to improve their lubricating power or their lubricity. These include rapeseed, linseed, soybean and sunflower oils or their esters (see Patents EP 635,558 and EP 605,857). However, one of the major disadvantages of these esters is their low lubricating power at a concentration of less than 0.5% by weight in the fuels.
The present invention aims to solve the problems encountered with the additives provided by the prior art, that is to say to improve the lubricating power of the desulphurized and partially dearomatized fuels, while remaining compatible with the other additives, in particular detergents, and the lubricating oils, in particular in not forming deposits, and while reducing the cost price, in particular by a lower additive content of markedly less than 0.5.
The subject of the present invention is the use as lubricity additive for improving the lubricating power of diesel and aviation fuels with a low sulphur content, that is to say with a sulphur content of less than or equal to 500 ppm, characterized in that the additive is composed of:
1) from 5 to 25% by weight of at least one glycerol monoester of following formula (IA) or (IB): 
xe2x80x83with R1 chosen saturated or unsaturated, linear or slightly branched, alkyl chains comprising from 8 to 24 carbon atoms and cyclic and polycyclic groups comprising from 8 to 60 carbon atoms;
2) from 35 to 75% by weight of at least one compound of formula (II) below: 
xe2x80x83R2 is a saturated or unsaturated, linear or slightly branched, alkyl chain comprising from 8 to 24 carbon atoms or a cyclic or polycyclic group comprising from 8 to 60 carbon atoms and X is chosen from (i) the groups OR0, wherein R0 being a hydrocarbon residue comprising from 1 to 8 carbon atoms, optionally substituted by one or more ester groups, and (ii) the groups deriving from primary and/or secondary amines or from alkanolamines with a linear or branched aliphatic hydrocarbon chain comprising from 1 to 18 carbon atoms, and
3) from 0.1 to 20% by weight, preferably from 5 to 20% by weight, of at least one glycerol diester of formula (IIIA) and/or (IIIB): 
xe2x80x83in which R3 and R4, which are identical or different, are chosen saturated or unsaturated, linear or slightly branched, alkyl chains comprising from 8 to 24 carbon atoms and cyclic and polycyclic groups comprising from 8 to 60 carbon atoms.
Preference is given, among the glycerol monoesters of formula (I) and the diesters of formula (III) with, respectively, R1 or R3 and R4 consisting of an alkyl chain, to the monoesters and diesters obtained from the oils of the group composed of lauryl oils originating from copra or palm, which are rich in saturated alkyl chains containing 12 to 14 carbon atoms, palmitic oils resulting from palm, lard or tallow, containing a major amount of saturated alkyl chains containing 16 carbon atoms, linoleic oils resulting from sunflower, maize or rape, containing a high content of linoleic acid, linolenic oils from linseed, comprising significant contents of triunsaturated alkyl chains containing from up to 18 carbon atoms, and ricinoleic oils resulting from the castor oil plant.
Among the glycerol monoesters and diesters obtained from polycyclic acids, the preferred monoesters and diesters comprise an R1 or R3 and/or R4 composed of at least two rings, each formed of 5 to 6 atoms, at most one of which is optionally a heteroatom, such as nitrogen or oxygen, and the others are carbon atoms, these two rings additionally having two carbon atoms in common, preferably vicinal, these said rings being saturated or unsaturated. These are preferably glycerol monoesters of natural resin acids obtained from the residues from the distillation of natural oils extracted from resinous trees, in particular resinous conifers.
Among these esters of resin acids according to the invention, preference is given to esters of abietic acid, of dihydroabietic acid, of tetrahydroabietic acid, of dehydroabietic acid, of neoabietic acid, of pimaric acid, of laevopimaric acid and of parastrinic acid.
By adjusting the operating conditions for partial hydrolysis of these oils, it is possible directly to obtain the mixture of glycerol monoalkyl esters/dialkyl esters.
According to another form of the invention, it is possible to prepare glycerol alkyl esters by an esterification reaction between the carboxylic acids described above and glycerol.
The esters and the amides of formula (II) can be easily obtained by reaction of an alcohol, amine and/or alkanolamine compound with an organic acid, such as oleic acid, or a simple ester, such as methyl oleate, the reaction being carried out under the conditions known per se by a person skilled in the art for esterification and amidation processes.
In a first embodiment, the alcohols used to obtain the compound (II) are chosen from the group composed of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol or 2-ethylhexanol, and/or oxyalkylated alcohols of formula R(Oxe2x80x94CH2xe2x80x94CHRxe2x80x2)nxe2x80x94OH, in which R is an alkyl group containing 1 to 6 carbon atoms, Rxe2x80x2 is hydrogen or an alkyl group containing 1 to 4 carbon atoms and n an integer varying from 1 to 5, such as methyl cellosolve, butyl cellosolve, butyl digol and 1-butoxypropanol.
In a second embodiment, the primary or secondary amines used to obtain the compound (II) are chosen from the group composed of methylamine, ethylamine, propylamine, butylamine, isobutylamine, 2-ethylhexylamine, decylamine, dodecylamine, stearylamine and oleylamine, N,N-diethylamine, N,N-dipropylamine, N,N-dibutylamine, N,N-di(2-ethylhexyl)amine, methyldecylamine, N-methyldodecylamine and N-methyloleylamine.
In a third embodiment, for the compound (II), use is made of alkanolamines chosen from amines containing 1 to 18 carbon atoms substituted by at least one hydroxylated, hydroxymethylated, hydroxyethylated or hydroxypropylated group, such as ethanolamine, diethanolamine, triethanolamine, isopropanolamine, diisopropanolamine, triisopropanolamine, N-methylethanolamine, tris(hydroxymethyl)aminomethane, (N-hydroxyethyl)methylimidazoline or (N-hydroxyethyl)heptadecenylimidazoline.
The additives obtained by physical mixing according to the invention are used to improve the lubricating power of diesel fuels for ground vehicle engines, optionally as a mixture with at least one oxygen-containing compound chosen from the group formed by alcohols, ethers and esters, as well as with any additive used to improve the quality of fuel, such as detergent, dispersing, antioxidizing and antifoaming additives or even biofuel.
A second subject of the invention corresponds to the fuels containing between 25 and 2500 ppm and preferably from 100 to 1000 ppm by weight of at least one additive used according to the invention dispersed in a diesel fuel which are defined by ASTM standard D-975.
The examples below are given by way of illustration of the invention but do not limit the scope thereof.